Question: 6 people can paint 4 walls in 49 minutes. How many minutes will it take for 9 people to paint 8 walls? Round to the nearest minute.
Solution: We know the following about the number of walls $w$ painted by $p$ people in $t$ minutes at a constant rate $r$ $w = r \cdot t \cdot p$ $\begin{align*}w &= 4\text{ walls}\\ p &= 6\text{ people}\\ t &= 49\text{ minutes}\end{align*}$ Substituting known values and solving for $r$ $r = \dfrac{w}{t \cdot p}= \dfrac{4}{49 \cdot 6} = \dfrac{2}{147}\text{ walls painted per minute per person}$ We can now calculate the amount of time to paint 8 walls with 9 people. $t = \dfrac{w}{r \cdot p} = \dfrac{8}{\dfrac{2}{147} \cdot 9} = \dfrac{8}{\dfrac{6}{49}} = \dfrac{196}{3}\text{ minutes}$ $= 65 \dfrac{1}{3}\text{ minutes}$ Round to the nearest minute: $t = 65\text{ minutes}$